A 6-year time series of physical parameters and particle fluxes collected by a mooring in Kongsfjorden (Svalbard) suggests that the subglacial and watershed run-off driven by air temperature are the main processes affecting the lithogenic supply. As the Arctic temperature rises, glacier material will increase accordingly. The winter inflow of warm Atlantic waters is progressively increasing, hampering the nutrient supply from the bottom waters and severely reducing the biological production.

We explored the relationship between organic carbon and mud (i.e. silt and clay) contents in seagrass ecosystems to address whether mud can be used to predict soil C content, thereby enabling robust scaling up exercises at a low cost as part of blue carbon stock assessments. We show that mud is not a universal proxy for blue carbon content in seagrass ecosystems, but it can be used to estimate soil Corg content when low biomass seagrass species (i.e. Zostera, Halodule and Halophila) are present.

We present a high-resolution multi-proxy study about the evolution of sea surface conditions along the last 2700 yr in the north-western Mediterranean Sea based on five sediment records from two different sites north of Minorca. The novelty of the results and the followed approach, constructing stack records from the studied proxies to preserve the most robust patterns, provides a special value to the study. This complex period appears to have significant regional changes in the climatic signal.

Residence times of particulate metals derived from aerosol deposition in the Sea Surface Microlayer of the Mediterranean Sea ranged from a couple of minutes (e.g., for Fe) to a few hours (e.g., for Cu). Microbial activity seems to play an important role in in this process and in the concentration and distribution of metals between diferent water layers.

The availability of macronutrients N and Si is of key importance to sustain life in the Southern Ocean. N and Si are available in abundance at the southern boundary of the Southern Ocean due to constant supply from the deep ocean. In the more northern regions of the Southern Ocean, a decline in macronutrient concentration is noticed, especially strong for Si rather than N. This paper uses a simplified biogeochemical model to investigate processes responsible for this decline in concentration.

This study brings further support to the premise that the prevalence of younger and thinner icescapes over older and thicker ones in the Canadian High Arctic favors the early development of under-ice microorganisms as well as their production of the climate-relevant gas dimethylsulfide (DMS). Given the rapid rate of climate-driven changes in Arctic sea ice, our results suggest implications for the timing and magnitude of DMS pulses in the Arctic, with ramifications for climate forecasting.

Hydrogen peroxide, H2O2, is formed naturally in sunlight-exposed water by photochemistry. At high concentrations it is undesirable to biological cells because it is a stressor. Here, across a range of incubation experiments in diverse marine environments (Gran Canaria, the Mediterranean, Patagonia and Svalbard), we determine that two factors consistently affect the H2O2 concentrations irrespective of geographical location: bacteria abundance and experiment design.

We investigated the spatial distribution of dissolved Fe during spring 2014, in order to understand the processes influencing the biogeochemical cycle in the North Atlantic. Our results highlighted elevated Fe close to riverine inputs at the Iberian Margin and glacial inputs at the Newfoundland and Greenland margins. Atmospheric deposition appeared to be a minor source of Fe. Convection was an important source of Fe in the Irminger Sea, which was depleted in Fe relative to nitrate.

Oxygen minimum zones (OMZs) are ocean areas severely depleted in oxygen as a result of physical, chemical, and biological processes. Biologically, organic material is produced in the sea surface and exported to deeper waters, where it respires. In the Bay of Bengal (BoB), an OMZ is present, but there are traces of oxygen left. Our study now suggests that this is because one key process, nitrogen fixation, is absent in the BoB, thus preventing primary production and consecutive respiration.

The influence of climate signals in the Pacific, especially the Pacific Decadal Oscillation and the North Pacific Gyre Oscillation, as well as El Niño–La Niña and an 18.6-year nodal tidal cycle on oxygen and nutrient trends is investigated. At different locations in the Pacific Ocean different climate signals dominate. Hence, not only trends related to warming but also the influence of climate signals need to be investigated to understand oxygen and nutrient changes in the ocean.

Satellite data and a remarkable set of in situ measurements show a main bloom of microscopic seaweed, the phytoplankton, in summer and a secondary bloom in December in the central equatorial Atlantic. They are driven by a strong vertical supply of nitrate in May–July and a shorter and moderate supply in November. In between, transport of low-nitrate water from the west explains most nitrate losses in the sunlit layer. Horizontal eddy-induced processes also contribute to seasonal nitrate removal.

Coccolithophores account for a major fraction of the carbonate produced in the world's oceans. However, their contribution in the subantarctic Southern Ocean remains undocumented. We quantitatively partition calcium carbonate fluxes amongst coccolithophore species in the Australian–New Zealand sector of the Southern Ocean. We provide new insights into the importance of species other than Emiliania huxleyi in the carbon cycle and assess their possible response to projected environmental change.

The arrangement of deep nutrient reservoirs is driven by large scale circulation features, however internal processes could also contribute at long terms.We propose to test this hypothesis in the western Mediterranean Sea, where diapycnal diffusion between intermediate and deep waters is enhanced, ultimately shaping the water column as thermohaline staircases.The estimation of nutrient fluxes induced by these processes showed their contribution to observed spatial pattern of the nutrient stocks.

We found that 24 % of the total diatoms community in the Arctic water column (450 m depth) was located below the photic layer. Healthy diatom communities in active spring–bloom stages remained in the photic layer. Dying diatom communities exported a large fraction of the biomass to the aphotic zone, fuelling carbon sequestration and benthic ecosystems in the Arctic. The results of the study conform to a conceptual model where diatoms grow during the bloom until silicic acid stocks are depleted.

In this study, we examine the responses of E. huxleyi to a future warmer and more thermally variable ocean. Elevated temperatures and thermal variation have negative effects on growth rate and physiology that are especially pronounced at high temperatures, but high-frequency thermal variation may reduce the risk of extreme high-temperature events. These findings have potentially large implications for ocean productivity and marine biogeochemical cycles under a future changing climate.

Around half of the global primary production (PP) is produced in the ocean. Here we quantified how much oceanic PP estimates would increase if we included the dark DIC fixation rates (which are usually excluded in the carbon-14 method) into the PP estimation. We found that the inclusion of dark DIC fixation would increase PP estimates by 5–22 %. This represents ca. 1.2 to 11 Pg C yr−1 of newly synthesized organic carbon available for the marine food web.

The Antarctic Ice Sheet is considered a possibly important but largely overlooked source of iron (Fe). Here we explore its fertilization capacity by evaluating the response of marine biogeochemistry to Fe release from icebergs and ice shelves in a global ocean model. Large regional impacts are simulated, leading to only modest primary production and carbon export increases at the scale of the Southern Ocean. Large uncertainties are due to low observational constraints on modeling choices.

The carbon isotopes in algae can be used to predict food sources and environmental change. We explore how dissolved carbon is taken up by algae in the South Atlantic Ocean and how this affects their carbon isotope signature. We find that cell size controls isotope fractionation. We use our results to investigate how climate change may impact the carbon isotopes in algae. We suggest a shift to smaller algae in this region would decrease the carbon isotope ratio at the base of the food web.

Recent studies suggest spatial variations of the marine particle flux length scale. Using a global biogeochemical ocean model, we investigate whether changes in particle size and size-dependent sinking can explain this variation. We address uncertainties by varying aggregate properties and circulation. Both aspects have an impact on the representation of nutrients, oxygen and oxygen minimum zones. The formation and sinking of large aggregates in productive areas lead to deeper flux penetration.

The remains of plankton rain down from the surface ocean to the deep ocean, acting to store CO2 in the deep ocean. We used a model of biology and ocean circulation to explore the importance of this process in different regions of the ocean. The amount of CO2 stored in the deep ocean is most sensitive to changes in the Southern Ocean. As plankton in the Southern Ocean are likely those most impacted by future climate change, the amount of CO2 they store in the deep ocean could also be affected.

The Indian Ocean subtropical gyre is a large oligotrophic area that is likely to adjust to continued warming by increasing stratification, reduced nutrient supply and decreasing biological production. In this study, we investigated concentrations of nutrients and stable isotopes of nitrate. We determine the lateral influence of water masses entering the gyre from the northern Indian Ocean and from the Southern Ocean and quantify the input of nitrogen by N2 fixation into the surface layer.

This study takes advantage of the GLODAPv2 database to investigate the processes driving the surface ocean dissolved inorganic carbon distribution, with the focus on its latitudinal gradient between the polar oceans and the low-latitude oceans. Based on our quantitative study, we find that temperature-driven CO2 gas exchange and high-latitude upwelling of DIC- and TA-rich deep waters are the two major drivers, with the importance of the latter not having been previously realized.

A strong El Niño event occurred in the Peruvian coastal region in 2015–2016, during which higher sea surface temperatures co-occurred with significantly lower sea-to-air fluxes of nitrous oxide, an important greenhouse gas and ozone depletion agent. Stratified water column during El Niño retained a larger amount of nitrous oxide that was produced via multiple microbial pathways; and intense nitrous oxide effluxes could occur when normal upwelling is resumed after El Niño.

Anthropogenic greenhouse gas emissions trigger complex climate feedbacks. Output form Earth system models provides a basis for related political decision-making. One challenge is to arrive at reliable model parameter estimates for the ocean biogeochemistry module. We illustrate pitfalls through which flaws in the ocean module are masked by wrongly tuning the biogeochemistry and discuss ensuing uncertainties in climate projections.

The GEOVIDE cruise (May–June 2014, R/V Pourquoi Pas?) aimed to provide a better understanding of trace metal biogeochemical cycles in the North Atlantic. As particles play a key role in the global biogeochemical cycle of trace elements in the ocean, we discuss the distribution of particulate iron (PFe). Lithogenic sources appear to dominate the PFe cycle through margin and benthic inputs.

We used surface water dissolved aluminium concentrations collected in four different GEOTRACES cruises to determine atmospheric deposition fluxes to the ocean. We calculate atmospheric deposition fluxes for largely under-sampled regions of the Atlantic Ocean and thus provide new constraints for models of atmospheric deposition. The use of the MADCOW model is of major importance as dissolved aluminium is analysed within the GEOTRACES project at high spatial resolution.

In this study, we investigate the evolution of CO2 uptake and ocean acidification in the North Atlantic Subpolar surface water. Our results show an important reduction in the capacity of the ocean to absorb CO2 from the atmosphere (1993–2007), due to a rapid increase in the fCO2 and associated with a rapid decrease in pH. On the contrary, data obtained during the last decade (2008–2017) show a stagnation of fCO2 (increasing the ocean sink for CO2) and pH.

Drivers motivating the evolution of calcifying phytoplankton are poorly understood. We explore differences in global ocean chemistry with and without calcifiers during rapid climate changes. We find the presence of phytoplankton calcifiers stabilizes the volume of low oxygen regions and consequently stabilizes the concentration of nitrate, which is an important nutrient required for photosynthesis. By stabilizing nitrate concentrations, calcifiers improve their growth conditions.

Dinitrogen fixation and primary production were investigated using stable isotope incubation experiments along two transects off the Western Iberian Margin in May 2014 close to the end of the phytoplankton spring bloom. We observed substantial N2 fixation activities (up to 1533 µmol N m-2 d-1) associated with a predominance of unicellular cyanobacteria and non-cyanobacterial diazotrophs, which seemed to be promoted by the presence of bloom-derived organic matter and excess phosphorus.

The ocean is a source of atmospheric carbon monoxide, a key component for the oxidizing capacity of the atmosphere. We use a global ocean biogeochemistry model to dynamically assess the oceanic CO budget and its emission to the atmosphere at the global scale. The total emissions of CO to the atmosphere are 4.0 Tg C yr−1. The oceanic CO emission maps produced are relevant for use by atmospheric chemical models, especially to study the oxidizing capacity of the atmosphere above the remote ocean.

Oceanographers try to understand the ocean’s role in the global carbon cycle. Trace levels of natural radionuclides can inform this connection and their half-lives provide an estimate of the timing of processes. We used the 210Po and 210Pb pair to examine the export of carbon from the surface ocean to depth along the GEOVIDE GEOTRACES cruise track. We found that the flux was regionally variable, that upwelling was an important regional factor, and that both large and small particles drove flux.

The use of high-resolution hydroacoustic and optic data acquired by an autonomous underwater vehicle can give us detailed sea bottom topography and valuable information regarding manganese nodules' spatial distribution. Moreover, the combined use of these data sets with a random forest machine learning model can extend this spatial prediction beyond the areas with available photos, providing researchers with a new mapping tool for further investigation and links with other data.

To better understand the impact of the Fukushima accident on commercial marine species, neon flying squid samples obtained from the NW Pacific in Nov 2011 were analyzed for a range of radionuclides. Elevated levels of Cs-134 and Ag-110m from the Fukushima accident were found in the samples, with an extremely high concentration ratio for Ag-110m. However, the radiological dose for squid living in the study area, and for human consumers of these squid, was far below the recommended dose limits.

We analyze data-constrained state estimates of the global marine iron cycle, a key control on the ocean's biological carbon pump. We develop new techniques for counting the iron's number of passages through the biological pump and link this number to the ocean's natural iron fertilization efficiency. We find that the majority of iron is not biologically utilized before being scavenged, and we identify the central equatorial Pacific as having the highest iron fertilization efficiency.

Oxygen-depleted regions of the Pacific Ocean are currently expanding, which is threatening marine habitats. Based on numerical simulations, we show that the decrease in the intensity of the trade winds and the subsequent slowdown of the oceanic currents lead to a reduction in oxygen supply. Our study suggests that the prevailing positive conditions of the Pacific Decadal Oscillation since 1975, a major source of natural variability, may explain a significant part of the current deoxygenation.

The GEOVIDE cruise (GEOTRACES Section GA01) was conducted in the North Atlantic Ocean and Labrador Sea in May–June 2014. In this special issue, results from GEOVIDE, including physical oceanography and trace element and isotope cyclings, are presented among 17 articles. Here, the scientific context, project objectives, and scientific strategy of GEOVIDE are provided, along with an overview of the main results from the articles published in the special issue.

Using a regional ocean model, we find that coccolithophore biomass in the Southern Ocean is highest in the subantarctic in late summer when diatom growth becomes limited by silicate. We show that zooplankton grazing is crucial to explain phytoplankton biomass distributions in this area and conclude that assessments of future distributions should not only consider physical and chemical factors (temperature, light, nutrients, pH), but also interactions with other phytoplankton or zooplankton.

This work examines the effect of salinity changes on the biogeochemistry of the coccolithophores with a palaeoproxy perspective. Although substantial changes in growth rate are observed between cells grown under various salinities, these physiological changes have no significant impact on the oxygen isotope composition of their biominerals. Thus, established coccolith δ18O / temperature calibrations are not complicated by salinity. By contrast, it does influence coccolith δ13C values.

A large anomalously warm water patch appeared in the NE Pacific in winter 2013–14 and persisted through 2016. Its effect on biological carbon export was determined using O2 and dissolved inorganic carbon data from a profiling float and a surface mooring. Results show the carbon export decreased after the first year when warmer water invaded and then returned to the previous value, with a similar trend in phytoplankton abundance and corresponding changes in phytoplankton community composition.

Organisms living in natural environments have to cope with constantly fluctuating conditions in order to compete and survive. Hereby, membrane lipids may play an integral role. This study demonstrates that the lipid repertoire and lipid modifications in marine picoplankton living in oxygen minimum zones may be larger than previously thought. The abundant presence of non-phosphorus lipids hint at nutrient limitation within deeper depths of the ocean, even though these are not considered as such.

The formation rates of oxygen to nitrogen anomalies in the subtropical North Pacific and North Atlantic were estimated from time series data. We find that vertically migrating phytoplankton, which traverse ~ 100–150 m in the upper ocean over days to acquire nutrients from waters at depth and return to the surface for photosynthesis, likely explain the observed anomalies and help sustain surface ocean productivity and the biological pump throughout the annual cycle in the subtropical ocean.

Methylmercury accumulates in marine organisms and is produced by bacterial processes in sediment systems. To date, the contribution of these processes to the marine water column is poorly understood. We measured noncellular production and breakdown of methylmercury in equatorial Pacific waters. We observed enhanced production in filtered waters that suggests noncellular processes result in rapid mercury transformations and, in turn, control methylmercury concentrations in the open ocean.

We investigated the surface particulate organic carbon export fluxes in the North Atlantic with the objective of better understanding the biological carbon pump. Our results highlighted that exports depended on the intensity and stage of the bloom, the phytoplankton size and community structures. After comparing with primary production, we concluded that, during our study, the North Atlantic behaves like most of the highly productive areas in the world's ocean, with a low export efficiency.

Humans have had a huge impact on the mercury cycle in the biosphere, but it is difficult to follow the mercury cycle because mercury has so many mobile forms, as gases in the atmosphere and solutes in water. Mercury isotopes constrain mercury fluxes and sources, because mercury has many stable isotopes, and different fractionation mechanisms have different fingerprints in those isotopic compositions. We present the first model of mercury isotopic composition in the ocean.

Phytoplankton biomass changed significantly in the North Atlantic north of 40° N over 1998–2007. With a physical-ecosystem model, we show that biomass increases in the northwest are due to reduced vertical mixing that partially relieves light limitation of phytoplankton. To the east, these circulation changes lead to fewer nutrients being supplied horizontally from the west. Relationships between these biomass variations and atmosphere and ocean physics are not straightforward.

The role of N and P released by copepods on biogeochemical cycles and the microbial community during the OUTPACE cruise was studied. In the presence of copepods, NH4+ and DON increase, and an enhanced remineralization was observed. A shift in active bacterial composition was observed, linked with changes in nutrient concentrations. Copepods can be a source of (in)organic compounds for bacterial communities that contribute to nutrient recycling and regenerated production in the photic zone.

Our paper provides an intensive overview of the artificial ocean iron fertilization (aOIF) experiments conducted over the last 25 years to test Martin’s hypothesis, discusses aOIF-related important unanswered open questions, suggests considerations for the design of future aOIF experiments to maximize their effectiveness, and introduces design guidelines for a future Korean Iron Fertilization Experiment in the Southern Ocean.

Abrupt climate changes in Earth’s history might have been triggered by magmatic intrusions into organic-rich sediments, which can potentially release large amounts of greenhouse gases. In the Guaymas Basin, vigorous hydrothermal venting at the ridge axis and off-axis inactive vents show that magmatic intrusions are an effective way to release carbon but must be considered as very short-lived processes in a geological sense. These results need to be taken into account in future climate models.

The Si biogeochemical cycle was studied during two oceanographic cruises in the tropical South Pacific in 2005 and 2015, between New Caledonia and the Chilean upwelling (8–34° S). Some of the lowest levels of biogenic silica stocks were found in the southern Pacific gyre, where Chlorophyll a concentrations are most depleted worldwide. Size-fractionated biogenic silica concentrations as well as Si kinetic uptake experiments revealed biological Si uptake by the picoplanktonic size fraction.

We measured two natural radio-isotopes, 210Po and 210Pb, in the dissolved and particulate phase along the GEOVIDE cruise track to try to understand the cycling of these isotopes across a diverse combination of currents, basins, and conditions in the North Atlantic Ocean. Other groups collected data on many other trace elements and isotopes in order to map them as part of the GEOTRACES program. We found that Po and Pb activity was concentrated on small particles and varied within/between basins.

It is projected that the summer–winter difference in pCO2 levels will be larger in the future. In this paper, we study the causes of this seasonal amplification of pCO2. We found that anthropogenic CO2 enhances the effect of seasonal changes in temperature (T) and dissolved inorganic carbon (DIC) on pCO2 seasonality. This is because the oceanic pCO2 becomes more sensitive to seasonal T and DIC changes when the CO2 concentration is higher.

The marine diazotrophic Cyanobacterium Trichodesmium from the Underwater Vision Profiler 5 is concentrated in the first 50 m in the western tropical Pacific Ocean (18–22° S, 160° E–160° W). Its contribution to Tchl a and zeaxanthin is 60 % in the Melanesian archipelago and 30 % in the Fijian archipelago. Its impact on UV–VIS radiance is a peculiar signal in the green and yellow and possibly associated with backscattering or phycoerythrin fluorescence from Trichodesmium.

IOC, IHO and BODC: Centenary edition of the GEBCO digital atlas, published on CD-ROM on behalf of the Intergovernmental Oceanographic Commission and the International Hydrographic Organization as part of the General Bathymetric Chart of the Oceans, Liverpool, UK, 2003.

UNEP/MAP/MEDPOL: Sub-Regional Assessment of the Status of Marine and Coastal Ecosystems and of Pressures to the Marine and Coastal Environment Eastern Mediterranean Sea UNEP(DEPI)/MEDWG.350/Inf.4, Barcelona, 37–38, 2010.

A multi-proxy approach is applied in surface sediments collected from deep slopes and basins (1018-4087 m depth) of the oligotrophic eastern Mediterranean Sea. This study sheds new light on the sources and transport mechanisms along with the impact of preservation vs. diagenetic processes on the composition of sedimentary organic matter in the deep basins of the oligotrophic eastern Mediterranean Sea.

A multi-proxy approach is applied in surface sediments collected from deep slopes and basins...